The present invention relates to a chipping-resistant coating compound composition for use in rust prevention of motor vehicles. It also relates to a chipping-resistant coating resin composition contained in the coating compound composition, and further relates to a process for forming a of film of the coating compound composition.
Polyester resins, amino resins or polyester resins/blocked isocyanate resins have been used to date on the sides of motor vehicles.
These resins have excellent chipping resistance. However, thick coated parts evolve foaming in the course of baking due to solvents in the coating compound. Also, preferential curing of coating-film surface causes drawbacks such as marked deterioration of appearance. It has hence been very difficult to apply thick coating films having a thickness of about 500 .mu.m or more.
The undersides of automobile floors have been primarily covered with polyvinyl chloride plastisol. Although the plastisol can provide thick coating films, it is inferior in adhesion to cation electrodeposition films and has the disadvantage of lowering chipping resistance after exposure to water.
Automotive coating is required sealing on the matched surfaces of steel plates. In this context the thickness of coating films increases to about 600 .mu.m at the overlapped part of coating films having 200 .mu.m in thickness. Consequently, it has been desired to provide a chipping-resistant coating resin composition which can be applied to form a thick coating film and an overlapped coating film and also has chipping-resistance when used as a thinner coating film of less than about 500 .mu.m in thickness.